- Anti-drug antibodies (ADAs) are antibodies the immune system makes against a medicine. Most bind without blocking the drug; a smaller subset, neutralizing antibodies, can block it.
- In tirzepatide's phase 3 trials, about half of participants developed ADAs, and about 2% developed antibodies that neutralized its activity, according to the US label.
- How closely a peptide resembles a human protein is a major driver. Liraglutide is about 97% identical to human GLP-1; exenatide about 53%. Exenatide's reported antibody rates are far higher.
- Immune genes matter too. In a 2020 study of anti-TNF drugs, carrying HLA-DQA1*05 roughly doubled the rate of antibody formation.
- No immunogenicity study has been published for BPC-157, TB-500 or most research peptides, so their antibody rates are unknown.
Peptides are proteins, and the immune system can learn to recognise a protein medicine as foreign. When it does, it makes anti-drug antibodies (ADAs). For approved peptide drugs this is measured in the trials and reported on the label. For research peptides it has mostly never been measured. Here is what the data show.
This page is education about the research record. It does not recommend any peptide, and it is not medical advice. Questions about a prescription drug belong with the prescriber.
How does the immune system make antibodies against a peptide?
Immune cells break proteins into fragments and display them on surface molecules called HLA. T cells scan those fragments, and if one looks foreign they help B cells start making antibodies against it.
Antibodies against a drug come in two broad kinds:
Binding antibodies
Attach to the drug without blocking the part that acts on its receptor. In the GLP-1 drug trials, most ADAs were of this kind and had no detectable effect on how well the drug worked at the group level.
Neutralizing antibodies
Attach to the active region and can stop the drug reaching its receptor. They are less common, and they are the kind that can reduce a drug's effect.
How often do approved GLP-1 drugs trigger antibodies?
Every approved GLP-1 drug was tested for immunogenicity before approval, and the results are on the US label. The rates vary widely, and the pattern lines up with how closely each drug resembles human GLP-1.
| Drug | Sequence identity to human GLP-1 | What the trials reported |
|---|---|---|
| Liraglutide (Victoza, Saxenda) | About 97% | Antibodies in a small, single-digit percentage of participants |
| Semaglutide (Ozempic, Wegovy) | About 94% | Antibodies in a small, single-digit percentage of participants |
| Tirzepatide (Mounjaro, Zepbound) | Dual GIP and GLP-1 agonist | About half developed ADAs; about 2% had antibodies that neutralized its activity |
| Exenatide (Byetta, Bydureon) | About 53% | Antibodies in a large share of participants, with reduced glucose control in some with high titres |
The comparison between liraglutide and exenatide is the clearest. Liraglutide was engineered from the human GLP-1 sequence; exenatide comes from a non-human peptide first found in venom and shares about half its sequence with human GLP-1. The drug that looks less like the body's own molecule triggers antibodies far more often.
Sequence identity to human GLP-1 for liraglutide and exenatide. The drug further from the human sequence has much higher reported antibody rates.
Tirzepatide shows that a high ADA rate is not the same as lost efficacy. About half of trial participants developed antibodies, yet the label reports that most were binding antibodies and that efficacy was maintained across the trial population.
Why do some people form antibodies and others not?
Part of the answer is immune genetics. HLA genes are among the most variable in the human genome, and different versions display different protein fragments.
The clearest human evidence comes from biologic drugs rather than peptides. In a 2020 study of people with Crohn's disease treated with anti-TNF antibodies (Sazonovs et al., Gastroenterology), carrying HLA-DQA1*05 roughly doubled the rate of antibody formation against the drug. FDA guidance on immunogenicity testing also lists patient factors, including genetic background, among the influences on antibody responses.
No study has tested whether HLA-DQA1*05, or any other genotype, changes antibody formation against a peptide drug or a research peptide.
What is known about antibodies to BPC-157 or TB-500?
Nothing measured. No immunogenicity study has been published for BPC-157, TB-500 or most other research peptides, because none has gone through the trials where this is tested. The general pattern from approved drugs, that sequences closer to human proteins tend to trigger fewer antibodies, has never been measured for these compounds.
Verdict: antibody formation against peptide drugs is real, measured and reported on the labels of approved GLP-1 drugs. Rates range from low single digits to about half of trial participants, and most antibodies do not block the drug. Sequence similarity to human proteins and HLA genetics both play a part. For research peptides, the rates are simply unknown.
Frequently asked questions
What are anti-drug antibodies?
Anti-drug antibodies are antibodies the immune system makes against a medicine it recognises as foreign. Most bind the drug without blocking it. A smaller subset, neutralizing antibodies, bind the active region and can reduce the drug's effect.
How often does tirzepatide trigger antibodies?
According to the US label, about half of participants in tirzepatide's phase 3 trials developed anti-drug antibodies, and about 2% developed antibodies that neutralized its activity. Efficacy was maintained across the trial population.
Why do some GLP-1 drugs trigger more antibodies than others?
Sequence similarity to human GLP-1 is a major factor. Liraglutide is about 97% identical to human GLP-1 and has low reported antibody rates. Exenatide, derived from a non-human peptide first found in venom, is about 53% identical and has much higher reported rates.
Do genes affect antibody formation against drugs?
Yes, for some drugs. In a 2020 study of anti-TNF drugs in Crohn's disease, HLA-DQA1*05 carriers formed antibodies at roughly twice the rate of non-carriers. No study has tested whether any genotype changes antibody formation against a peptide.
Are antibodies to BPC-157 or TB-500 known?
No. No immunogenicity study has been published for either compound, so no antibody rate has been measured.
This article is for informational and educational purposes only. It reports what published research found; it is not medical advice, it does not diagnose, treat, cure or prevent any disease, and nothing in it is a dose or a recommendation to use any compound. Talk to a licensed clinician about any medical decision.